The Six transports, carrying 2,000 men of the Kanno Detachment of the 48th Infantry Division, land troops near Vigan, but are bombed and strafed by five Boeing B-17 "Flying Fortresses" and escorting Seversky P-35A "Guardsman" and Curtiss P-40B "Kittyhawk" fighters of the U. S. Army's Far East Air Force. During the action, a minesweeper is sunk and two transports are so damaged they have to be beached.

23 January 1942: The Invasion of Balikpapan, Borneo:
Storms protect the invasion force until it is almost to Balikpapan. At 1525, nine Dutch Martin Model 166 (B-10) bombers from Samarinda attack and hit transports TATSUGAMI and NANA MARUs. The latter is abandoned and later sinks. TATSUGAMI MARU continues on to Balikpapan. At 2045, Hirose's invasion convoy arrives and anchors off Balikpapan. At 2130, the transports begin disembarking troops.

10 March 1942:
Reassigned to Vice Admiral Takahashi's Southwest Area Fleet's newly formed Third Southern Expeditionary Fleet in Special Base Force 31 organized at Manila. CH-10 engages in the blockade of Manila Bay.

8 August 1942:
CH-10 and CH-11 arrive at Saiki after conducting an anti submarine sweep in the Saiki area.

11 August 1942:
CH-10 and CH-11 depart Saiki on an anti submarine sweep. They join up with CH-12 which has been on a training exercise.

12 August 1942:
CH-10, CH-11 and CH-12 all arrive back at Saiki.

13 August 1942:
CH-10 and CH-11 depart Saiki on an anti submarine. Over the following few days both ships conduct a series of sweeps and patrols of the Bungo Suido returning to Sukumo to resupply as necessary.

24 August 1942:
CH-10, CH-11 and CH-12 arrive at Saiki.

28 August 1942:
CH-10 alone departs Saiki and resumes patrols and submarine sweeps of the Bungo Suido homebasing at Sukumo as necessary.

1 September 1942:
Departs Sukumo and arrives later that day at Saiki.

4 September 1942:
Departs Saiki.

6 September 1942:
Arrives at Sukumo.

7 September 1942:
Departs Sukumo and later that day arrives at Saiki.

10 September 1942:
Departs Saiki and later that day arrives at Kure.

14 September 1942:
Departs Kure and later that day arrives at Saiki.

22 September 1942:
CH-10 and CH-11 depart Saiki on patrol.

24 September 1942:
Both CH-10 and CH-11 arrive at Sukumo and depart later that day.

19 November 1943:
Northern Marianas. In the early morning hours, Cdr (MOH, posthumously) Samuel Dealey's (USNA ’30) USS HARDER (SS-257) makes radar contact off the port quarter of the convoy. Dealey makes an "end around" then submerges 15,000 yards ahead of the convoy. He waits until YUZUKI passes 800 yards across his stern then fires his six bow torpedoes at two large transports and gets five hits. At 0415, HOKKO MARU sinks at 0415 at 22-27N, 147-15E with 24 crewmen and 21 passengers KIA. Dealey swings USS HARDER around and fires his four stern tubes. At 0435, UDO MARU is hit and badly damaged. Five crewmen are KIA.

YUZUKI takes UDO MARU in tow, but at 1040, the transport's hull splits and the aft part of the ship sinks. CHIYO MARU takes up towing CH-10 and heads for Chichi-Jima with FUKUE. Later, NIKKO MARU is ordered back to assist in the tow of UDO MARU. At 1850, NIKKO MARU arrives back on the scene, but experiences great difficulty trying to tow UDO MARU. Finally, the wreck is abandoned and sinks a few hours later.

The escorts counterattack and drive USS HARDER deep under a thermocline layer of cold water. Dealey's crew counts 64 depth depth charges dropped over the next five hours during which they reload all tubes. USS HARDER surfaces early in the afternoon and takes up the chase again. That night, Dealey closes to 1,000 yards of the convoy and fires four Mark 14-3A steam torpedoes at a transport, but they all run deep and pass under the target. Dealey makes another "end around" and submerges 12,000 yards ahead of the convoy. He sets up and at 2355, fires three bow torpedoes and gets one hit in NIKKO MARU's stern.

20 November 1943:
The Japanese get NIKKO MARU's pumps running and efficiently control the flooding. In the early morning hours, USS HARDER fires three more stern torpedoes at her, but they all miss. Out of torpedoes, a frustrated Sam Dealey departs the area, but NIKKO MARU later loses her battle with the sea and sinks. 15 crewmen are KIA.